2/Theory of Operation
2-22 1503-0151-000 3/27/97
Gas Inlet Valve Drive Circuit
This circuit consists of a LM2952IM low-dropout regulator providing a regulated 5
Volts to the inlet valve when enabled by the microprocessor. The /SHUTDOWN
pin of the regulator provides on/off control.
This regulator has an output current of 250mA. It has an internal current limit of
530mA max. This keeps the output under 10VA in a single fault condition and
meets the 10VA requirements of IEC 601-2-13.
A current sensing circuit is included to allow the processor to monitor the inlet valve
current via the A/D converter system and detect fault conditions.
Front Panel Display Interface
All signals to and from the Front Panel are protected from ESD through the use of
transient suppression devices and appropriate filtering. All of these signals are
routed through a single connector from the microcontroller board to the front panel
assembly.
EL Display Controller
The S-MOS SED1351F Flat Panel display controller drives 480 horizontal pixels
by 240 vertical pixels of the front panel EL display. Ferrite beads filter the signals
from the display controller to the display.
Video Display Memory
This memory consists of one high speed 32K x 8 CMOS static RAM directly con-
nected to the SED1351F display controller, but mapped into 68340 memory space.
Membrane Switch Inputs
These signals are electronically debounced and sampled by the 68340 processor.
LED Driver Outputs
The ac on LED are turned on directly from the ac power applied and the mechan-
ical ventilation LED is controlled by the glue logic. Both LEDs require no interven-
tion from the microcontroller.
Rotary Encoder Input
This quadrature signal is debounced and routed to a quadrature clock converter
which interrupts the 68340 processor at each detent position.
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